Box 16 is to report foreign income. Many have received the K-1 with box 16 checked knowing they will not be receiving a K-3 or received a K-3 with it listed as US income. If you know you are not going to have foreign income or do not believe you will have foreign income, you can go ahead and file your returns and uncheck box 16. However, if you receive a K-3 with foreign income listed you will need to amend your returns to include the K-3 income.
If you know you are going to receive a K-3 with foreign income it is best to file for an extension and file when all documents are received. However, as stated above, if you do go ahead and file and receive the K-3 with foreign income, you can amend your returns to add in the additional income.
@GeoffS
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